Place the mushrooms in a food processor and blend until finely chopped.
Heat the oil in a pan and fry the chopped mushrooms for 2 minutes. Add the ginger and garlic and cook for 1 minute. Remove from the heat and transfer to a mixing bowl.
Once the mixture has cooled, stir in the chicken mince, chives, soy sauce, cornflour and black pepper.
Keep the wrappers covered with a damp towel to prevent them from drying out. Place 1 tablespoon of chicken mixture in the middle of one wrapper and lightly brush the rim of the wrapper with the beaten egg. Fold the wrapper in half, enclosing the filling, to form a semicircle. Pinch the edges firmly to seal, pleating the front side to form several folds.
Holding sealed edges, stand each dumpling on a plate and gently press to flatten the bottom of each wonton. Repeat with remaining wrappers and filling. Sprinkle the sesame seeds over the wontons. Steam the wontons, in batches, for 5 – 7 minutes.
Whisk all of the dipping sauce ingredients together and serve with the wontons.*Cook’s note – find wonton wrappers in the freezer section of Asian supermarkets